The present invention relates to circuits and methods for detecting high-speed signals.
The present invention provides a method and a circuit that detect the presence of a high-speed signal, such as a high-speed differential signal, based on a software-programmable signal amplitude threshold. In one embodiment, when the amplitude threshold is exceeded, a current is generated to charge a capacitor. The voltage on the capacitor is compared to a second pre-set voltage in a low-speed comparator, which provides an output voltage indicating detection of the high-speed signal. In one embodiment, a high-speed differential signal operating at 3.125 Gbits per second can be detected.
According to one embodiment of the present invention, a high-speed signal detection circuit includes a capacitor, and a detection circuit receiving a high-speed signal and a threshold voltage. The detection circuit charges the capacitor when the high-speed signal has an amplitude exceeding the threshold voltage by a predetermined amount. In one embodiment, the high-speed signal detection circuit further includes a comparator receiving a reference voltage and coupled to the capacitor. The comparator provides an output signal having two binary states, the output signal transitioning between the binary states when a voltage on the capacitor exceeds the reference voltage. The high-speed signal can be a differential signal.
In one embodiment of the present invention, the high-speed signal detection circuit includes first and second transistors each having a source terminal and a drain terminal being coupled respectively to a terminal of the capacitor and a predetermined voltage, and a gate terminal coupled to one end of the differential signal.
In one embodiment of the present invention, the high-speed signal detection circuit generates the reference voltage by tapping a string of resistors.
In one embodiment of the present invention, the high-speed signal detection circuit generates a second reference voltage from the string of resistors. The reference voltage is selected by activating one of a number of switches, each switch being coupled to receive one of the first and second reference signals. In one implementation, the switches can be made software programmable.